In a closing method, a work piece constituted by a metal pipe material is rotated and a die is pressed against the work piece while the work piece is heated. Thus, the work piece undergoes plastic deformation as it gradually approaches the die.
A closing machine used in the closing operation comprises an outer diameter chuck that holds an outer peripheral surface of the work piece, and a chuck spindle that drives the outer diameter chuck to rotate together with the work piece. The work piece is closed by pressing the rotating die against the work piece at an offset to the rotating work piece.
The closing method and closing machine are disclosed in JP2002-153930A.
In a conventional closing machine, a sensor for detecting the position of the work piece and a sensor for detecting the temperature of the die are provided near the processed portion of the work piece, and the closing operation is performed automatically in accordance with detection signals from these sensors.
However, in a conventional closing machine, lampblack is generated from the processed portion of the work piece when the die and work piece are heated, and this lampblack may soil the lens and so on of the sensors, leading to a reduction in the detection precision of the sensors.
It is therefore an object of this invention to provide a closing method and a closing machine with which the detection precision of a sensor can be maintained.